Method of casting steel in a shell mold



J. T. BAKER Nov. 5, 1968 METHOD OF CASTING STEEL IN A SHELL MOLD Filed Feb.

United States Patent 015cc 3,409,069 Patented Nov. 5, 1968 3,409,069 METHOD OF CASTING STEEL IN A SHELL MOLD James T. Baker, Munster, Ind., assignor to Amsted Industries Incorporated, Chicago, 11]., a corporation of New Jersey Filed Feb. 1, 1966, Ser. No. 524,145 2 Claims. (Cl. 164138) ABSTRACT OF THE DISCLOSURE Molten steel is poured into a shell mold the external surface of which is in contact with wet sand or is in a wet condition by water and a wetting agent whereby a water vapor atmosphere is generated at the surface of the mold which contacts the molten steel and said atmosphere is maintained until the surface of the casting which contacts the mold has permanently solidified thereby affording an improved condition of said casting surface.

This invention relates generally to shell molding and more particularly to the elimintation of surface defects in steel castings produced in conventional shell molds.

Shell molds, as well known in the art, are generally formed of a mixture of zircon or silica sand and a thermosetting phenolic resin either in powder form or in a solvent. The mixture of sand and resin is packed around a heated pattern to set the resin to bind the sand particles into a shell mold with a cavity of the configuration of the pattern.

As molten steel is poured into such a mold, an atmosphere is created therein which is carburizing in its effect on the molten steel and causes carburization of the surface of the casting. The surface which is in contact with the mold Wall freezes to define a skin around the casting. Carburization of this skin reduces its melting temperature. During the solidification and cooling of the casting, opposing forces are set up in the casting with the result that the carburized skin is highly susceptible to cracking.

It is therefore an object of this invention to provide a method of shell molding steel castings wherein the tendency of the skin of the casting to crack is substantially, if not completely, eliminated.

Another object of this invention is to provide a method of casting steel in shell molds wherein cracking of the skin of the casting is substantially, if not completely, prevented.

These and other objects and advantages of this invention will become apparent from a reading of the following detailed description When taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a cross-sectional view in elevation of a shell mold and associated structure, and

FIGURE 2 is a view similar to FIGURE 1 illustrating an alternative embodiment of this invention.

Referring now to the drawings, reference numeral denotes a conventional shell mold formed of two halves 12 and 14 which when placed together form a cavity 16 into which molten metal is poured. The cavity 16 is illustrated schematically in the drawings because the contour of the casting is immaterial to the successful operation of this invention. The two mold halves 12 and 14 are positioned in a box 18 or other similar receptacle. Sand 20 which has been thoroughly wet with water is placed around the two mold halves and may be vibrated or packed into place in order to support the mold in its upright position.

If desired, the wet sand 20 may be eliminated and the mold supported by braces 22 as is shown in FIGURE 2. In such event, water 24 containing a suitable wetting agent is poured over the outside of the mold 10 to wet substantially, if not all, of the exterior surface 26 of the mold 10. Suitable wetting agents are, for example, ethyl alcohol or sodium dioctyl sulfosuccinate in a water and 5% lower alcohol solution.

Molten metal is then poured into the mold 10 through an opening (not shown) in the conventional manner. The castings take from the mold 10 after the casting had solidified exhibited substantially less tendency to crack in service than did those castings taken from molds which were not contacted by either water or wet sand.

The water as in FIGURE 2 or from the sand vaporizes at the temperature present in the casting operation and passes through the surface 26 of the mold 10. This water vapor occupies the space between the mold walls 28 and the casting which space is created as the casting begins to cool. Preferably sufficient water is provided to maintain the water vapor in this space until the surface of the casting has permanently solidified.

It should be apparent from a reading of the foregoing description that various modifications may be made without departing from the spirit and scope of this invention as defined in the following claims.

I claim:

1. A method of casting steel comprising pouring water and a wetting agent over the externalsurface of a shell mold and pouring molten steel into said shell mold, said water generating a water vapor atmosphere at the surface of the mold which contacts the molten steel and maintaining said water vapor atmosphere until the surface of the casting which contacts the mold has permanently solidified.

2. A method of casting steel comprising packing water wet sand around the external surface of a shell mold and pouring molten steel into said shell mold, said water generating a water vapor atmosphere at the surface of the mold which contacts the molten steel and maintaining said water vapor atmosphere until the surface of the casting which contacts the mold has permanently solidified.

References Cited UNITED STATES PATENTS 2,507,608 5/1950 Barnes 164-72 X 2,518,055 8/1950 Olsen et al. 164138 X 2,753,608 7/1956 Nolan 164-138 X 2,858,589 11/1958 Bean l64-138 3,354,935 11/1967 Mann 164-126 J. SPENCER OVERHOLSER, Primary Examiner. E. MAR, Assistant Examiner. 

